Associating photos to the faces of a cube
You need to:

Create 6 different materials (Since you have 6 different images you need to create one material per image). 

Have each of the materials use an image as texture.

In Edit mode you need to select a face and assign a material to it.



Repeat that to all of the other faces until each one has a material and each material is using the texture you want. 

 



For greater control on how the textures are mapped on the mesh, you need to unwrap the mesh to create UV maps.